13.6: Hazards from Earthquakes

Overview

Earthquakes are among nature’s most destructive phenomena, and there are numerous hazards associated with them. Ground shaking itself leads to falling structures, making it the most dangerous hazard. The intensity of ground shaking depends on several factors, including the size of the earthquake, the duration of shaking, the distance from the epicenter, and the material the ground is made of. Solid bedrock will not shake much during a quake, rendering it safer than other ground materials. Artificial fill refers to areas that have been filled in for construction and/or waste disposal (think of a hill that gets cleared for a shopping mall – the soil that was removed is dumped somewhere else as artificial fill). Sediment is not compacted in areas of artificial fill, but compaction will occur during the shaking of an earthquake, leading to structural collapse. Artificial fill sediments behave similarly to water-saturated sediments. As they shake, they may experience liquefaction, in which the sediments behave like a fluid. Normally, friction between grains holds them together. Once an earthquake occurs, water surrounds every grain, eliminating the friction between them and causing them to liquefy (Figure 13.14). This can be very dangerous. Seismic waves will amplify as they come in contact with these weaker materials, leading to even more damage.

Other hazards associated with earthquakes include fire (as gas lines rupture), which may be difficult to combat as water lines may also be ruptured. The vast majority of damage during the 1906 San Francisco earthquake was due to fire. Earthquakes can trigger tsunamis, large sea waves created by the displacement of a large volume of water during fault movement. The Sumatra-Andaman earthquake in 2004 triggered a tsunami in the Indian Ocean that resulted in 230,000 deaths. Earthquakes can trigger landslides in mountainous areas and initiate secondary hazards such as fires, dam breaks, chemical spills, or even nuclear disasters like the one at Fukushima Daiichi Nuclear Power Plant in Japan. Earthquake-prone areas can take steps to minimize destruction, such as implementing strong building codes, responding to the tsunami warning system, addressing poverty and social vulnerability, retrofitting existing buildings, and limiting development in hazardous zones.

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